The present invention relates to an apparatus for changing reproduction speed of speech sound wherein digital signals of speech sound are reproduced by changing only speed thereof without changing pitch thereof.
In case of reproducing, for example, messages recorded on a magnetic tape in an answer-phone or contents of a lecture or the like recorded by a tape recorder at high speed, the faster tape feed speed results in the higher pitch of the reproduced speech sound. However, when pitch changes from the original speech sound, characteristics (voice quality, male voice, female voice, etc.) belonging to the original speech sound are damaged, and in this respect, a reproduction speed changing apparatus wherein speech sound is reproduced by changing only the reproduction speed at a constant magnification without changing pitch of the original speech sound has been developed.
Meanwhile, in case of hearing a speech, it is difficult to catch the words at both the too fast speed and the too slow speed, so that the contents of the speech cannot be well grasped. In general, it is said that when reproduction speed becomes three times faster, the words cannot be completely caught by even an ordinary person without any handicap. In a conventional reproduction speed changing apparatus, however, since reproduction speed is changed at a constant magnification, there is a limitation for changing magnification in the case when it is intended to increase the reproduction speed within a range in which the contents of speech can be well grasped. Accordingly, a period of time required for reproduction of speech data could have not been remarkably reduced, even if a conventional reproduction speed changing apparatus is employed for the purpose of reproducing speech signals at high speed (quick hearing).